Downlink transmission method and user terminal equipment

ABSTRACT

Disclosed is a method for communication by a base station in a wireless communication system, including transmitting, to a user equipment (UE), downlink control information (DCI) including information on a modulation and coding scheme (MCS) for processing downlink data using an MCS table among a plurality of tables, and transmitting, to the UE, the downlink data, wherein each of the plurality of MCS tables indicates modulation orders and code rates, wherein the plurality of MCS tables comprises a first MCS table which supports 256 quadrature amplitude modulation (QAM) and a second MCS table which does not support 256 QAM, and wherein a number of MCS indexes in the first MCS table is equal to a number of MCS indexes in the second MCS table.

PRIORITY

This is a Continuation of U.S. patent application Ser. No. 16/659,085,filed in the U.S. Patent and Trademark Office on Oct. 21, 2019, which isa Continuation of U.S. patent application Ser. No. 16/561,498, filed inthe U.S. Patent and Trademark Office on Sep. 5, 2019, now U.S. Pat. No.10,609,717, issued Mar. 31, 2020, which is a Continuation of U.S. patentapplication Ser. No. 16/263,793, filed in the U.S. Patent and TrademarkOffice on Jan. 31, 2019, now U.S. Pat. No. 10,448,413, issued on Oct.15, 2019, which is a Continuation of U.S. patent application Ser. No.16/031,317, filed with the U.S. Patent and Trademark Office on Jul. 10,2018, now U.S. patent Ser. No. 10/455,594, issued on Oct. 22, 2019,which is a Continuation of U.S. patent application Ser. No. 14/916,399,filed with the U.S. Patent and Trademark Office on Mar. 3, 2016, nowU.S. Pat. No. 10,257,841, issued on Apr. 9, 2019, which is a NationalPhase Entry of PCT International Application No. PCT/KR2014/002289,which was filed on Mar. 18, 2014, and claims priority to Chinese PatentApplication No. 201310394991.1, which was filed on Sep. 3, 2013, ChinesePatent Application No. 201310424907.6, which was filed on Sep. 17, 2013,and Chinese Patent Application No. 201310515958.X, which was filed onOct. 28, 2013, the content of each of which is incorporated herein byreference.

1. FIELD OF THE DISCLOSURE

The present invention relates to wireless communication system, and moreparticularly to a downlink transmission method and a user terminalequipment.

2. BACKGROUND OF THE RELATED ART

In 3GPP LTE system, each wireless frame has a length of 10 ms, and isdivided into ten equally sized subframes. A downlink transmission timeinterval (TTI) is defined in one subframe. As shown in FIG. 1, eachdownlink subframe includes two slots. For a normal cyclic prefix (CP)length, each slot contains 7 OFDM symbols; for an extended cyclic-prefixlength, each slot contains 6 OFDM symbols. In each subframe, the front n(n is equal to 1, 2 or 3) OFDM symbols are to transmit downlink controlinformation including a physical downlink control channel (PDCCH) andother control information; the remaining OFDM symbols are to transmitPhysical Downlink Shared Channel (PDSCH) or enhanced PDCCH (E PDCCH).The resource allocation granularity is a physical resource block (PRB).One PRB contains 12 consecutive subcarriers in frequency and correspondsto a time slot in time. In one subframe, two PRBs respectively locatedin two slots of the subframe while occupying same subcarriers arereferred to as a PRB pair. In each PRB pair, each resource elements (RE)is the smallest unit of time-frequency resources, i.e., a subcarrier infrequency and an OFDM symbol in time. RE can be used for differentfunctions, respectively. For example, some RE can be used to transmitcell-specific reference signal (CRS), user-specific demodulationreference signal (DMRS) and channel quality indicator reference signal(CSI-RS), etc.

In LTE system, multiple transmission modes are defined for transmittingdata. For example, for downlink direction, there are closed loopmultiple-input multiple-output (MIMO) transmission mode, open loop MIMOtransmission mode, transmit diversity transmission, and so on. For onetransmission mode, the system configures a normal downlink controlinformal (DCI) format which is to complete normal data transmissionunder this kind of transmission mode. Meanwhile, the base station alsoconfigures a User Equipment (UE) to detect one kind of fallback DCIformat. The fallback DCI format usually has fewer bits, adopts a moreconservative way to schedule data, such as transmit diversity orsingle-antenna sending data, and thus has high reliability.

In LTE system, DCIs which are sent to different UEs or have differentfunctions can be independently coded and transmitted. When performingphysical resource mapping on PDCCH, taking control channel Element (CCE)as a unit; when performing physical resource mapping on EPDCCH, takingenhanced CCE (ECCE) as a unit. In following description, when it is notneeded to specifically distinguish PDCCH and EPDCCH, they can becollectively referred to as (E)PDCCH; accordingly, CCE and ECCE can becollectively referred to as (E)CCE. Specifically, modulation symbols ofone (E)PDCCH can be mapped to L (E)CCE, where L can be equal to 1, 2, 4,16 or 32, and L can also be known as aggregation level of (E)PDCCH.(E)PDCCH fixed adopts QPSK modulation method; according to bit number ofcontrol information and link condition of UE, the base station canselect aggregation level of (E)CCE for sending (E)PDCCH.

In the existing LTE versions, downlink data transmission based on QPSK,16 Quadrature Amplitude Modulation (QAM) and 64 QAM can be supported.Table 1 shows indexes of modulation coding scheme (MCS) and transportblock size (TBS) which are used for downlink transmission. Specifically,in the existing LTE versions, in DCI information, 5 bits are used toindicate MCS and TBS information, in which 29 code words simultaneouslyindicate modulation mode and TBS, the last 3 code words only indicatemodulation mode, while TBS information can be obtained according toprevious DCI information and be used for retransmission of PDSCH.

TABLE 1 MCS and TBS for PDSCH transmission MCS index modulation I_(MCS)order Q_(m) TBS index I_(TBS) 0 2 0 1 2 1 2 2 2 3 2 3 4 2 4 5 2 5 6 2 67 2 7 8 2 8 9 2 9 10 4 9 11 4 10 12 4 11 13 4 12 14 4 13 15 4 14 16 4 1517 6 15 18 6 16 19 6 17 20 6 18 21 6 19 22 6 20 23 6 21 24 6 22 25 6 2326 6 24 27 6 25 28 6 26 29 2 reserved 30 4 31 6

Accordingly, in order to support the base station scheduling downlinkPRB resource, UE needs to report channel status indication (CSI)information including channel quality indicator (CQI) information. Table2 shows modulation mode and code rate, etc. of each CQI index.Specifically, in the existing LTE version, 4 bits are used to report CQIinformation. Consistent with MCS configuration in the existing LTEversion, in CQI measurement, only situations in which downlink datatransmissions based on QPSK, 16 QAM and 64 QAM can be currentlysupported.

TABLE 2 CQI information CQI code rate × index coding 1024 efficiency 0invalid value 1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4QPSK 308 0.6016 5 QPSK 449 0.8770 6 QPSK 602 1.1758 7 16 QAM 378 1.47668 16 QAM 490 1.9141 9 16 QAM 616 2.4063 10 64 QAM 466 2.7305 11 64 QAM567 3.3223 12 64 QAM 666 3.9023 13 64 QAM 772 4.5234 14 64 QAM 8735.1152 15 64 QAM 948 5.5547

In LTE version 12, in order to add a peak downlink transmission rate ofa small cell, one possible candidate technique is to support PDSCHtransmission based on 256 QAM modulation. In a typical networkconfiguration, for example, uses a macro base station on lowerfrequencies to achieve large coverage; and sets some small base stationson higher frequencies to achieve hotspot coverage. Since the small basestation uses high frequency point, its propagation characteristicsdetermine inter-cell interference is small and there is not interferencefrom the macro base station, thus, signal to interference and noiseratio of UE in smaller cell can be very high and can sufficientlysupport downlink transmission based on 256 QAM. In order to introducethe support for 256 QAM, it is needed to modify processing way of MCSand CQI in the existing LTE specifications and solve a series ofresulting problems.

SUMMARY

The present application discloses a downlink transmission method anduser terminal equipment, which can support 256 QAM modulation andoptimize performance of downlink transmission.

In order to achieve the above object, the present application provides amethod for communication by a base station in a wireless communicationsystem, including transmitting, to a UE, DCI including information on anMCS for processing downlink data using an MCS table among a plurality oftables, and transmitting, to the UE, the downlink data, wherein each ofthe plurality of MCS tables indicates modulation orders and code rates,wherein the plurality of MCS tables comprises a first MCS table whichsupports 256 QAM and a second MCS table which does not support 256 QAM,and wherein a number of MCS indexes in the first MCS table is equal to anumber of MCS indexes in the second MCS table.

Also provided is a base station comprising a transceiver, and acontroller coupled to the transceiver, wherein the controller isconfigured to transmit, to a UE, DCI including information on an MCS forprocessing downlink data using an MCS table among a plurality of tables,and transmit, to the UE, downlink data, wherein each of the plurality ofMCS tables indicates modulation orders and code rates, wherein theplurality of MCS tables comprises a first MCS table which supports 256QAM and a second MCS table which does not support 256 QAM, and wherein anumber of MCS indexes in the first MCS table is equal to a number of MCSindexes in the second MCS table.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a subframe;

FIG. 2 is a flowchart of a downlink transmission method of the presentapplication;

FIG. 3 is a schematic diagram showing different CSI processes usesdifferent CQI tables;

FIG. 4 is a schematic diagram showing different downlink subframe setscorresponding to different MCS tables; and

FIG. 5 is a schematic diagram of a user terminal equipment of thepresent application.

DETAILED DESCRIPTION

In order to make the objective, technical solution and advantage of thepresent application clearer, the present application will be describedin further detail hereinafter with reference to accompanying drawings.

The existing version of LTE only supports three kinds of modulationmodes including QPSK, 16 QAM and 64 QAM. These 3 kinds of modulationmodes cover transmission requirements under a variety of typicalsituations. That is, supporting transmissions based on QPSK when channelconditions are very poor, and supporting transmissions based on 64 QAMwhen the channel conditions are very good. Only for some scenes ofparticularly high SINR, downlink transmission can be performed based on256 QAM, thereby improving downlink peak rate. In fact, even in case ofgood channel conditions, considering dynamic changes of interference,fast fading and slow fading of links, corner effects, etc., link statusof UE is not always capable of performing downlink transmission based on256 QAM; that is to say, it is needed to support switching betweenmodulation modes such as 256 QAM, 64 QAM, 16 QAM and QPSK. In somesituations, MCS table or CQI table of the existing version of LTE isalready suitable for downlink transmission of UE; while in some othersituations, MCS table or CQI table which are newly defined forsupporting 256 QAM is more suitable for processing downlink transmissionof UE.

FIG. 2 is specific flowchart of a downlink transmission method of thepresent application. As shown in FIG. 2, the method includes:

Block 201: UE receiving configuration information sent from a basestation, and accordingly adjusting CQI table and MCS table.

In the block 201, in default situation, UE uses CQI table and MCS tableof the existing version of LTE, this ensures that UE can successfullyaccess a base station of the existing version of LTE and a base stationof the new version of LTE. In fact, since a base station does not knowwhether UE supports transmissions of 256 QAM before UE reports itscapabilities, thus, the system must work according to the existingversion of LTE at this moment. For UE supporting 256 QAM, when the basestation knows that link status of UE can support transmissions of 256QAM, a high layer signaling can be adopted to configure UE to work in amode of supporting 256 QAM. At this moment, both of MCS table and CQItable will be changed relative to the existing LTE standard, so as toprovide support for 256 QAM, and related parameters needs to be set. Infollowing block 202 and block 203, the related parameters which may needto be set will be described in details.

Block 202: UE measuring and reporting downlink channel qualityinformation to the base station; here, UE can report the CQI informationaccording to a backward compatible CQI table or a CQI table whichsupports 256 QAM modulation;

In the block 202, a CQI table of the existing LTE version can beextended to add support for 256 QAM. Two prefer ways of configuring CQItable are described as follows.

A first way is to define one or more new CQI tables which support 256QAM, based on CQI table of the existing LTE version. Recording a numberof the new CQI tables is N, then, N+1 CQI tables can be supported in thenew version of LTE system. When it is needed to configure UE to use 256QAM, the base station uses a high layer signaling to configure UE to useCQI tables supporting 256 QAM. For example, if defining only one new CQItable which supports 256 QAM, 1 bit signaling can be used to configureUE to use CQI table of the existing LTE standard or the CQI table whichsupports 256 QAM.

Assuming that average channel status of one UE is very good and cansupport 256 QAM, then, the possibility that the same UE is in a very badchannel status in short time is usually small. Therefore, one way ofgenerating CQI table which supports 256 QAM can be to remove some CQIitem having lower modulation order from the existing CQI table and additems which uses 256 QAM. A preferred way of the present application isdescribed as follows. Here, consistent with the existing CQI table, CQIindex 0 can be used to indicate invalid CQI value; or, in a tablesupporting 256 QAM, all 16 values indicate valid CQI information.

In the first kind of ways, one way of generating CQI table whichsupports 256 QAM can be to remove some CQI item having the lowestspectrum efficiency from the existing CQI table, renumber the remainingCQI items for QPSK/16 QAM/64 QAM in return, and then add items for 256QAM. For example, removing 5 items having the lowest index from theexisting CQI table, 5 items which support 256 QAM can be addedaccordingly. Here, some CQI items refer to one or more CQI items.

For situations in which channels of UE can support 256 QAM, in order todeal with the case of deep fading occurring on the channels of UE, itmay be necessary to retain some QPSK items having lower coding rate. Inthis way, when configuring CQI table of 256 QAM, another way ofgenerating CQI table which supports 256 QAM can be to, on the premise ofkeeping some QPSK items having lowest or lower coding rate in theexisting CQI table unchanged, remove some QPSK, even 16 QAM items,renumber the remaining CQI items for QPSK/16 QAM/64 QAM in return, andthen add items for 256 QAM. For example, removing indexes 2˜6 from theexisting CQI table, 5 items which support 256 QAM can be addedaccordingly.

Still another way of generating CQI table which supports 256 QAM can beto, based on the existing CQI table, increase feedback granularity ofCQI items having lower spectrum efficiency; for example, for CQI itemshaving lower spectrum efficiency, retaining only one of every two CQIitems, i.e., removing CQI items 2, 4, 6 and 8; renumber the remainingCQI items for QPSK/16 QAM/64 QAM in return and then add items for 256QAM. Application of this way, the CQI table which supports 256 QAM,still can cover all channel statuses, just increasing granularity of CQIitems having lower spectrum efficiency.

All the above ways are to remove some items from the existing CQI tableand renumber the remaining CQI items; when defining new CQI table whichsupports 256 QAM, some items to be removed from CQI table can also bedirectly replaced with items of 256 QAM, without changing modulationorders and spectrum efficiencies represented by other CQI items of CQItable. Specifically, corresponding to the above ways of removing CQItable items, some CQI items having lower spectrum efficiency of theexisting CQI table can be replaced with items of 256 QAM; or, on thepremise of keeping some QPSK items having lowest or lower coding rate inthe existing MCS table unchanged, some QPSK even 16 QAM items can bereplaced with items of 256 QAM; or, based on the existing CQI table,increasing feedback granularity of CQI items having lower spectrumefficiency, for example, for CQI items having lower spectrum efficiency,one of every two CQI items can be replaced with items of 256 QAM.

In the above ways of generating CQI table which supports 256 QAM, CQIitems having lower spectrum efficiency can be reduced to indicate 256QAM. In fact, CQI table in the existing standard can support 64 QAM andcoding rate as high as 0.92, on the premise that UE can support 256 QAM,the performance of using 64 QAM and coding rate as high as 0.92 may benot optimized, and they may be replaced with some CQI items which basedon 256 QAM transmission. That is to say, in addition to the abovementioned reducing some CQI items having lower spectrum efficiency toindicate 256 QAM, one or more items of 64 QAM having highest coding ratecan be removed to indicate 256 QAM. Specifically, one manner of removingone or more items of 64 QAM to indicate 256 QAM, can be used separatelyto generate new CQI table, and can also be combined with the abovementioned manner of reducing some CQI items having lower spectrumefficiency to indicate 256 QAM to generate new CQI table.

A second kind of ways is to add items corresponding to 256 QAM in CQItable of the existing version of LTE, thereby obtaining a long CQI tableof a length more than 16 items, i.e., the long CQI table containsinformation of more than 16 items of CQI indexes. At this moment, sincethe length of the CQI table is more than 16 items, thus, it is needed toreconsider reporting manner of CQI information.

One reporting manner can be to add number of bits through which UEreports CQI information; for example, using 5 bits to feedback CQI.

Or, a bit number of 4 bit CQI information can also remain unchanged, andthus CQI reporting mechanism of the existing version of LTE can bedirectly be reused. Further, at the time feeding back 4 bit CQIinformation, UE can feed back an offset value for indicating an actualindex of CQI information reported by the base station in the long CQItable which supports 256 QAM modulation. For example, recoding a valueof 4 bit CQI is c and an offset value is v, CQI value c which is equalto 0 can still represent invalid CQI value; while for CQI value c isequal to 1˜15, an actual index of CQI fed back by UE is CQI index c+v ofthe above long CQI table. The offset value v and rank indication (RI)information of CSI feedback information of UE can be joint coded andfeed back at a same timing position.

Or, 4 bit CQI can also remain unchanged, and thus the CQI reportingmechanism of the existing version of LTE can be directly be reused. Whenit is needed to configure UE to use 256 QAM, the base station uses ahigh layer signaling to configure an offset value v of CQI table for UE,and UE extracts 16 CQI items from the above long CQI table according tothe offset value v so as to form a CQI table which actually configuresUE. In the actual configuration CQI table, CQI value 0 can stillrepresent invalid CQI value; while CQI value c (c is equal to 1˜15) canbe mapped in turn to CQI index c+v of the above long CQI table.

In the existing version 10 of LTE, in order to support eICIC technique,downlink subframes of a cell can be divided into two sets, and channelstatuses of the two are different. Accordingly, CSI information can befed back for the two subframe sets, respectively. That is, the basestation can configure UE to report feedback information of the twosubframe sets, respectively. Average SINR levels of the above multiplesubframe sets are usually different. As shown in FIG. 3, taking eICIC asexample, one subframe set configured with ABSF corresponding to macrobase station, that is, interference on a smaller cell from the macrobase station is smaller, thus, SINR of UE in smaller cell can be veryhigh and may be suitable for using the modulation mode of 256 QAM. Forthe other subframe set, since the macro base station sends downlinkcontrol and downlink data, thus, SINR of UE is smaller and may not besuitable for using the modulation mode of 256 QAM.

The present application provides, when the base station configuresmultiple subframe sets of UE, configuring information of CQI table usedby each subframe set, respectively. If defining new table for 256 QAM,then, in the present application, UE is configured to use CQI table ofthe existing version of LTE or new CQI table which supports 256 QAM,according to SINR situation of this subframe set. If defining the abovelong CQI table, then, in the present application, UE is configured toselect an offset value v of CQI index from the long CQI table, accordingto SINR situation of this subframe set. For example, CQI value 0 canstill represent invalid CQI value; while CQI value c (c is equal to1˜15) can be mapped in turn to CQI index c+v of the above long CQItable. In this way, when the base station configures CSI reportingmanner for UE, the base station can configure information of CQI tableused in each subframe set, respectively. Accordingly, UE receivesinformation of CQI table configured by the base station for eachsubframe set, respectively, measures channel status for each subframeset, and feeds back CQI information according to CQI table configured bythe base station for this subframe set.

In the version 11 of LTE, in order to support data transmission of CoMP,the base station further supports configuring UE to report feedbackinformation of multiple CSI processes, and each CSI process can furtherbe divided into two subframe sets. In conclusion, the existing LTEsystem already supports configuring UE to feed back feedback informationof multiple CSI processes and multiple subframe sets. Average SINRlevels of the above multiple CSI processes and multiple subframe setsare usually different. In some CSI processes and subframe sets, SINR ofUE can be very high and may be suitable for using the modulation mode of256 QAM; while in other CSI processes and subframe sets, SINR of UE issmaller and may not be suitable for using the modulation mode of 256QAM.

The present application provides, when the base station configuresmultiple CSI processes of UE, configuring information of CQI table usedin each CSI process, respectively. If defining new table for 256 QAM,then, in the present application, UE is configured to use CQI table ofthe existing version of LTE or new CQI table which supports 256 QAM,according to SINR situation of this CSI process. If defining the abovelong CQI table, then, in the present application, UE is configured toselect an offset value v of CQI index from the long CQI table, accordingto SINR situation of this CSI process. For example, CQI value 0 canstill represent invalid CQI value; while CQI value c (c is equal to1˜15) can be mapped in turn to CQI index c+v of the above long CQItable. In this way, when the base station configures CSI reportingmanner for UE, the base station can configure information of CQI tableused in each CSI process, respectively. Accordingly, UE receivesinformation of CQI table configured by the base station for each CSIprocess, respectively, measures channel status for each CSI process, andfeeds back CQI information according to CQI table configured by the basestation for this CSI process.

The present application further provides, when the base stationconfigures multiple CSI processes and multiple subframe sets of UE,configuring information of CQI table used in each CSI process and byeach subframe set, respectively. If defining new table for 256 QAM,then, in the present application, UE is configured to use CQI table ofthe existing version of LTE or new CQI table which supports 256 QAM,according to SINR situation of one CSI process and one subframe set. Ifdefining the above long CQI table, then, in the present application, UEis configured to select an offset value v of CQI index from the long CQItable, according to SINR situation of one CSI process and one subframeset. For example, CQI value 0 can still represent invalid CQI value;while CQI value c (c is equal to 1˜15) can be mapped in turn to CQIindex c+v of the above long CQI table. In this way, when the basestation configures CSI reporting manner for UE, the base station canconfigure information of CQI table used in each CSI process and by eachsubframe set, respectively. Accordingly, UE receives information of CQItable configured by the base station for each CSI process and eachsubframe set, respectively, measures channel status for each CSI processand each subframe set, and feeds back CQI information according to CQItable configured by the base station for this CSI process and thissubframe set.

Block 203: UE receiving downlink scheduling information sent from thebase station, receiving and processing accordingly downlink data sentfrom the base station according to MCS information of DCI included inthe downlink scheduling information. Here, UE can process MCSinformation of DCI information according to a backward compatible MCStable or a MCS table which supports 256 QAM modulation.

In the block 203, an MCS table of the existing LTE version can beextended to add support for 256 QAM. Two prefer ways of configuring MCStable are described as follows.

A first kind of ways is to define one or more new MCS tables whichsupport 256 QAM based on MCS table of the existing version of LTE.Recording a number of the new MCS tables is N, then, N+1 MCS tables canbe supported in the new version of LTE system. Here, base stationssupporting 256 QAM can be divided into different levels. For example, asimple device only supports using 256 QAM in a not high encoding rate;while a complex device supports using 256 QAM in high encoding rate.Different MCS tables of 256 QAM can be configured for base stationswhich are of different levels and supports 256 QAM, respectively. Thisis one reason why defines multiple MCS tables which supports 256 QAM inabove. Or, in order to simplify the design, only one general new MCStable can be defined for all the base stations which support 256 QAM.When it is needed to configure UE to use 256 QAM, the base station usesa high layer signaling to configure UE to use MCS table which supports256 QAM.

Assuming that average channel status of one UE is very good and cansupport 256 QAM, then, the possibility that the same UE needs to adopt amodulation mode of lower modulation order is usually small. Therefore,one way of generating MCS table which supports 256 QAM can be to removesome MCS items having lower modulation order from the existing MCS tableand add items which uses 256 QAM. A preferred way of the presentapplication is described as follows. Here, consistent with the existingMCS table, the largest MCS values can only indicate modulation orderwhile not contain TBS information. The following description mainlyrefers to other MCS items which simultaneously indicate modulation orderand TBS.

In the first kind of ways, one way of generating MCS table whichsupports 256 QAM can be to remove some QPSK items having the lowestcoding rate from the existing MCS table, renumber the remaining MCSitems for QPSK/16 QAM/64 QAM in return starting from 0, and then additems for 256 QAM. For example, removing 5 items having the lowest indexfrom the existing MCS table, 5 items which support 256 QAM can be addedaccordingly.

For situations in which channels of UE can support 256 QAM, in order todeal with the case of deep fading occurring on the channels of UE, itmay be necessary to retain some QPSK items having lower coding rate. Inthis way, when configuring MCS table of 256 QAM, another way ofgenerating MCS table which supports 256 QAM can be to, on the premise ofkeeping some QPSK items having lowest or lower coding rate in theexisting MCS table unchanged, remove some QPSK, even 16 QAM items,renumber the remaining MCS items for QPSK/16 QAM/64 QAM in return, andthen add items for 256 QAM. For example, removing indexes 2˜6 from theexisting MCS table, 5 items which support 256 QAM can be addedaccordingly. Here, some MCS items refer to one or more MCS items.

Moreover, in existing MCS table, some MCS items are actually directlycorresponding to CQI items in CQI table, while other MCS items can beobtained through interpolation, thus, still another way of generatingMCS table which supports 256 QAM can be to remove MCS items obtainedthrough interpolation and whose spectrum efficiencies are within aspecified range (such as MCS items having lower spectrum efficiency)from the existing MCS table, renumber the remaining MCS items forQPSK/16 QAM/64 QAM in return starting from 0, and then add items for 256QAM. For example, removing indexes 1, 3, 5, 7 and 9 from the existingMCS table, 5 items which support 256 QAM can be added accordingly.

In fact, there is a corresponding relationship between CQI items of CQItable and MCS items of MCS table, thus, if removing some CQI items fromthe existing CQI tale when generating CQI table which supports 256 QAM,then accordingly, removing MCS items corresponding to the removed CQIitems from the existing MCS table, renumber the remaining MCS items forQPSK/16 QAM/64 QAM in return, and then add items for 256 QAM.

All the above ways are to remove some items from the existing MCS tableand renumber the remaining MCS items; when defining new MCS table whichsupports 256 QAM, some items to be removed from MCS table can also bedirectly replaced with items of 256 QAM, without changing modulationorders and TBS represented by other MCS items of MCS table.Specifically, corresponding to the above ways of removing MCS tableitems, QPSK items having lower coding rate of the existing MCS table canbe replaced with items of 256 QAM; or, on the premise of keeping someQPSK items having lowest or lower coding rate in the existing MCS table,some QPSK even 16 QAM items can be replaced with items of 256 QAM; or,MCS items obtained through interpolation and having lower spectrumefficiencies in the existing MCS table can be replaced with items of 256QAM; or, consistent with the way of generating CQI table which supports256 QAM, MCS items in the existing MCS table corresponding to theremoved CQI items can be replaced with items of 256 QAM; or, since MCSindex 0, i.e., I_(MCS)=0, has other special purpose, thus, redefiningI_(MCS)=0 as indicating 256 QAM modulation mode can be avoided and oneor more other MCS items with I_(MCS)>0 can be replaced with itemsindicating 256 QAM. The present invention does not specifically limitusing which MCS items with I_(MCS)>0 to indicate 256 QAM modulationmode. Here, when using the transmission mode of dual transmission block(TB), for example, in DCI formats 2, 2A, 2B, 2C and 2D, I_(MCS)=0 andrv_(idx)=1 can be set for one corresponding TB to indicate that this TBis not currently transmitted. If I_(MCS)=0 is reused to indicate 256 QAMmodulation mode, it will result in that rv_(idx)=1 cannot be used forHARQ retransmission, thereby affecting performance of 256 QAM datatransmission, thus, the MCS index with I_(MSC)=0 cannot be used toindicate 256 QAM modulation mode.

This way can ensure that confusion of MCS information in DCI will notoccur when configuring or reconfiguring downlink transmission mode.According to LTE system design, for each downlink transmission mode, UEsimultaneously detects two kinds of DCI formats, i.e., normal format andfallback format. In this method, when the network configures UE to useMCS table supporting 256 QAM, the two kinds of DCI formats cansimultaneously use MCS table supporting 256 QAM. For some MCS itemscontained in new MCS table supporting 256 QAM, the representedmodulation orders and TBS have the same definition as that ofcorresponding MCS indexes in the existing MCS table, thus, whenconfiguring or reconfiguring downlink transmission mode, so long asusing fallback DCI format and consistent MCS items of the two tables,confusion of MCS information in DCI can be avoided.

In the above ways of generating MCS table which supports 256 QAM, MCSitems having lower modulation order can be reduced to indicate 256 QAMmodulation mode. In fact, MCS table in the existing standard can support64 QAM and coding rate as high as 0.92, on the premise that UE cansupport 256 QAM, the performance of using 64 QAM and coding rate as highas 0.92 may be not optimized, and they may be replaced with some MCSitems which based on 256 QAM transmission. That is to say, in thepresent application, in addition to the above mentioned reducing someMCS items having lower modulation order to indicate 256 QAM, one or moreitems of 64 QAM having highest coding rate can be removed to indicate256 QAM modulation mode and corresponding TBS. Specifically, one mannerof removing one or more items of 64 QAM to indicate 256 QAM, can be usedseparately to generate new MCS table, and can also be combined with theabove mentioned manner of reducing some MCS items having lowermodulation order to indicate 256 QAM to generate new MCS table.

Further, in existing MCS table, there are some MCS items which haveequal spectrum efficiencies and different modulation modes. That is, MCSindexes 10 and 11 have equal spectrum efficiencies, but they adopt QPSKand 16 QAM, respectively; MCS indexes 16 and 17 have equal spectrumefficiencies, but they adopt 16 QAM and 64 QAM, respectively. One of thetwo MCS having equal spectrum efficiencies can be removed, therebyobtaining one code word for indicating 256 QAM transmission. Forexample, one of two MCS having equal spectrum efficiencies, which haslower modulation order, can be removed. Adoption of this method, twocode words can be obtained for indicating 256 QAM transmission.

A second kind of ways is to add items corresponding to 256 QAM in MCStable of the existing version of LTE, thereby obtaining a long MCS tableof a length more than 32 items, i.e., the long MCS table containsinformation of more than 32 items of MCS indexes. At this moment, sincethe length of the MCS table is more than 32 items, thus, it is needed toreconsider reporting manner of MCS information.

One reporting manner can be to add number of bits occupied by CQIinformation in DCI format; for example, using 6 bits to support MCSinformation.

Or, 5 bit MCS can also remain unchanged, and thus the DCI format of theexisting version of LTE can be directly be reused. When it is needed toconfigure UE to use 256 QAM, the base station uses a high layersignaling to configure an offset value v of MCS table for UE, and UEextracts 32 MCS items from the above long MCS table according to theoffset value v so as to form a MCS table which actually configures UE.For example, in the actual configuration CQI table, consistent withstructure of the existing MCS table, MCS values 28, 29, 30 and 31 in DCIindicate modulation orders 2, 4, 6 and 8, respectively (i.e.,corresponding to QPSK, 16 QAM, 64 QAM and 256 QAM, respectively); MCSvalue m (m is equal to 0˜27) can be mapped in turn to MCS index m+v ofthe above long MCS table. Corresponding to base stations which are ofdifferent levels and support using 256 QAM, UE can be configured withdifferent offset values v, thereby optimizing performance of downlinklink.

The ways of generating MCS table which supports 256 QAM are describedabove. For UE supporting 256 QAM, adoption of MCS table of the existingLTE standard or MCS table which supports 256 QAM can be configured. Insome situations, MCS table of the existing version of LTE has alreadysuitable for downlink transmission of UE; while in some othersituations, MCS table which are newly defined for supporting 256 QAM ismore suitable for improving peak downlink transmission rate of UE. Oneway of configuring MCS table of the existing LTE standard or MCS tablewhich supports 256 QAM according to the present application is describedbelow.

According to LTE system design, for each downlink transmission mode, UEsimultaneously detects two kinds of DCI formats, i.e., normal format andfallback format. The normal DCI format is to complete normal datatransmission under this kind of transmission mode. For situations ofneeding to configure UE to use 256 QAM, obviously, the normal DCI formatis able to support 256 QAM. The fallback DCI format usually has fewerbits, has high reliability and supports switching between downlinktransmission modes. So, the pursuit of peak downlink speed is not themain purpose of the fallback DCI format.

In the present application, for normal DCI format and fallback DCIformat detected by UE, different MCS tables can be respectively used.Specifically, for UE configured to support 256 QAM, MCS field of normalDCI format can use MCS table which supports 256 QAM, i.e., high layersignaling can be used to configure using one of MCS table of theexisting LTE standard and MCS table supporting 256 QAM; while MCS fieldof fallback DCI format is still consistent with the existing LTEstandard, i.e., uses MCS table of the existing LTE standard. When thebase station schedules downlink data transmission, according to selectednormal DCI format or fallback DCI format, according to the method of thepresent application, the base station selects MCS table to configure MCSof DCI. Accordingly, when UE detects (E)PDCCH in blind, if UE detects(E)PDCCH of normal DCI format in blind, assuming that the high layersignaling configures using MCS table supporting 256 QAM, UE can parseMCS information of DCI according to new MCS table which supports 256QAM; otherwise, UE can parse MCS information of DCI according to MCStable of the existing LTE standard; if UE detects (E)PDCCH of fallbackDCI format in blind, UE can parse MCS information of DCI according toMCS table of the existing LTE standard.

Adoption this way, no matter whether UE is configured with downlinktransmission of 256 QAM, fallback DCI format of UE is consistent withthe existing LTE standard, thereby ensuring that confusion of MCSinformation in DCI will not occur when configuring or reconfiguringdownlink transmission mode.

According to specification of version 11 of LTE, for transmission mode10, the system can configure 4 different kinds of configurationinformation of RE mapping and quasi-co-location (QCL) of PDSCH, and uses2 bits of DCI format to indicate current PPDSCH transmission is whichkind of RE mapping and QCL configuration. For each of the different REmapping and QCL configuration, its target physical layer transmissiontechnology may be different, for example, joint transmission (JT) orCoordinated scheduling/beamforming (CS/CB). Using different transmissiontechnologies, link statuses are also different. For example, when usingJT, SINR may be higher than CS/CB, so that it may be possible to use MCStable supporting 256 QAM when using JT; while using CS/CB, it is onlysuitable to using the existing MCS table.

The present application provides that, when configuring Remapping andQCI configuration of PDSCH for UE, MCS tables used corresponding to eachRE mapping and QCL configuration are simultaneously configured,respectively. When the base station schedules downlink datatransmission, after selecting RE mapping and QCL configuration of PDSCHto be used by UE, configures MCS field of DCI according to MCS tablewhich configures this RE mapping and QCL configuration. Accordingly,after UE detects one (E)PDCCH in blind, determines MCS table accordingto RE mapping and QCL configuration of PDSCH indicated by (E)PDCCH, andparses MCS information of DCI.

According to LTE system design, UE needs to detect in blind (E)PDCCHsent form the base station within two search space, i.e., common searchspace (CSS) and UE-specific search space (USS). (E)PDCCH transmitted inUSS is usually to trigger UE specific PDSCH transmission; while CSS isto send some cell-common (E)PDCCHs. Further, for DCI formats havingequal bit numbers in USS and CSS, (E)PDCCH of CSS can also trigger UEspecific PDSCH transmission. For UE configured to support 256 QAM,(E)PDCCH of USS is required to be able to support 256 QAM; while(E)PDCCH of CSS is not required to use MCS table supporting 256 QAM. Or,for UE configured to support 256 QAM, (E)PDCCH of USS is required to beable to support 256 QAM; for CSS, it can be configured by different MCStables according to purpose of (E)PDCCH sent by the CSS.

In the present application, MCS table to be used can be determinedaccording to whether (E)PDCCH detected by UE is in USS or CSS.Specifically, for UE configured to supporting 256 QAM, MCS tablesupporting 256 QAM can be used for (E)PDCCH in USS, i.e., high layersignaling can be used to configure using one of MCS table of theexisting LTE standard and MCS table supporting 256 QAM; MCS table of theexisting LTE standard can be fixed used for (E)PDCCH in CSS. When thebase station schedules downlink data transmission, for (E)PDCCH in USSand CSS, MCS table selected according to the method of the presentapplication can be used to configure MCS field of DCI. Accordingly, whenUE detects in blind (E)PDCCH, for (E)PDCCH in USS, assuming that thehigh layer signaling configures using MCS table supporting 256 QAM, MCSinformation of DCI can be parsed according to MCS table supporting 256QAM, otherwise, MCS information of DCI can be parsed according to MCStable of the existing LTE standard; for (E)PDCCH in CSS, MCS informationof DCI can be parsed according to MCS table of the existing LTEstandard.

Or, for UE configured to supporting 256 QAM, MCS table supporting 256QAM can be used for (E)PDCCH in USS, i.e., high layer signaling can beused to configure using one of MCS table of the existing LTE standardand MCS table supporting 256 QAM; for (E)PDCCH in CSS, if its DCI iscell specific, such as scheduling broadcast information, paginginformation or RACH response message (RAR), then (E)PDCCH uses MCS tableof the existing LTE standard. For (E)PDCCH in CSS, if its DCI is UEspecific, then (E)PDCCH can use MCS table supporting 256 QAM. When thebase station schedules downlink data transmission, for (E)PDCCH in USSand CSS, using MCS table selected according to the method of the presentapplication to configure MCS field of DCI. Accordingly, when UE detectsin blind (E)PDCCH, for (E)PDCCH in USS, assuming that the high layersignaling configures using MCS table supporting 256 QAM, MCS informationof DCI can be parsed according to MCS table supporting 256 QAM; for(E)PDCCH in CSS, if its DCI is cell specific, then MCS information ofDCI can be parsed according to MCS table of the existing LTE standard;for (E)PDCCH in CSS, if its DCI is UE specific, assuming that the highlayer signaling configures using MCS table supporting 256 QAM, then MCSinformation of DCI can be parsed according to MCS table supporting 256QAM; otherwise, MCS information of DCI can be parsed according to MCStable of the existing LTE standard.

In LTE system, one (E)PDCCH is an aggregation of one or more (E)CCE.Generally, when downlink channel quality of UE is good, a smalleraggregation level can be adopted; while downlink channel quality of UEis poor, a larger aggregation level can be used. Accordingly, fordownlink data transmission, when downlink link quality is good, 256 QAMmodulation mode may be adopted; while when downlink link quality ispoor, 256 QAM modulation mode usually cannot be adopted.

In the present application, MCS table used by DCI can be determinedaccording to aggregation level of (E)PDCCH. For example, (E)PDCCH withan aggregation level smaller than K can use new MCS table which supports256 QAM; (E)PDCCH with an aggregation level greater than K uses theexisting MCS table. When the base station schedules downlink datatransmission, determines an aggregation level of (E)PDCCH according todownlink link status of UE, and selects MCS table according to themethod of the present application to configure MCS field of DCI.Accordingly, after UE detects (E)PDCCH in blind, UE can parse MCS fieldof DCI according to the aggregation level of (E)PDCCH to obtainmodulation mode and TBS of base station scheduling.

In LTE system, two types of EPDCCH are defined, i.e., localized EPDCCHand distributed EPDCCH. Generally, localized EPDCCH is suitable forsituations in which the base station can obtain precise channel stateindication (CSI) information of different frequency subbands of UE, soas to obtain frequency scheduling gain; correspondingly, when the basestation does not have precise CSI information of UE, the base stationhas to distribute EPDCCH in multiple PRB pairs for sending, so as toobtain frequency diversity gain, i.e., distributed EPDCCH. In case ofthe base station sending localized EPDCCH, since CSI information isprecise, thus, 256 QAM can be used to further improve downlink peakrate. While in case of the base station sending distributed EPDCCH, CSIinformation is usually not precise, MCS table of the existing LTEstandard can provide good performance.

In the present application, MCS table used by DCI can be determinedaccording to types (localized or distributed) of EPDCCH. Specifically,EPDCCH candidates in a localized EPDCCH set can be configured to use newMCS table supporting 256 QAM, i.e., high layer signaling can be used toconfigure using one of MCS table of the existing LTE standard and MCStable supporting 256 QAM; while EPDCCH candidates in a distributedEPDCCH set can be configured to use existing MCS table. When the basestation schedules downlink data transmission, types (localized ordistributed) of EPDCCH can be selected according to downlink link statusof UE, and MCS table can be selected according to the method of thepresent application to configure MCS field of DCI. Accordingly, after UEdetects EPDCCH in blind, UE can parse MCS field of DCI according totypes (localized or distributed) of EPDCCH in accordance with the methodof the present application to obtain modulation mode and TBS of basestation scheduling.

In version 11 of LTE, supporting configuring UE with 2 EPDCCH sets. Fordownlink transmission mode 10, RE mapping and QCL configuration of eachEPDCCH set is consistent with one RE mapping and QCL configuration ofPDSCH. For each RE mapping and QCL configuration of PDSCH, its targetphysical layer transmission technology may be different, accordingly,its link statuses are also different. For example, when using JT, SINRmay be higher than CS/CB, so that it may be possible to use MCS tablesupporting 256 QAM when using JT. In this way, there can be a certaincorresponding relationship between EPDCCH set and link status whentransmitting PDSCH.

In the present application, each EPDCCH set of UE can be configured touse different MCS tables, respectively, i.e., when configuringparameters of the each EPDCCH set, the each EPDCCH set can be furtherconfigured to use one of MCS table of the existing LTE standard and MCStable supporting 256 QAM. When the base station schedules downlink datatransmission, DCI information can be transmitted in an EPDCCH candidateof one EPDCCH set of UE, MCS field of DCI can be configured according toMCS table configured by selected EPDCCH set. Accordingly, after UEdetects (E)PDCCH in blind, UE can determine MCS table according to theEPDCCH set to which the EPDCCH belongs, and parse MCS field of DCI.

In the version 10 of LTE, in order to support eICIC technique, downlinksubframes of a cell can be divided into two sets, and channel statusesof the two are different. As shown in FIG. 4, a subframe set configuredwith ABSF corresponds to macro base station, that is, interference on asmaller cell from the macro base station is smaller, thus, SINR of UEcan be very high and may be suitable for using the modulation mode of256 QAM. For the set of other subframes, since the macro base stationsends downlink control and downlink data, thus, SINR of UE is smallerand may not support the modulation mode of 256 QAM.

In the present application, the network can divide downlink subframesinto multiple sets, for example, different downlink subframe sets havedifferent degrees of interference; for each downlink subframe set,configures MCS table used by DCI which schedules downlink datatransmission of each downlink subframe set. If defining new table for256 QAM, then, in the present application, UE is configured to use MCStable of the existing version of LTE or new MCS table which supports 256QAM, according to SINR situation of each downlink subframe set. Ifdefining the above long MCS table, then, in the present application, UEis configured to select an offset value v of MCS index from the long MCStable, according to SINR situation of each downlink subframe set. AfterUE receives the above configuration information of MCS table fordifferent downlink subframe sets, when detecting DCI format schedulingdownlink transmission of one downlink subframe set, UE can parsemodulation mode and TBS of base station scheduling according to MCStable configured for downlink subframe set by network.

The present application also provides a user terminal equipment whichcan be used to implement the above downlink transmission method. FIG. 5is a schematic diagram of a user terminal equipment of the presentapplication. As shown in FIG. 5, the equipment includes: a CQIinformation measuring and reporting unit, a downlink schedulinginformation receiving unit and a downlink data receiving and processingunit.

The CQI information measuring and reporting unit is configured tomeasure and report downlink channel quality indicator (CQI) informationto a base station. Here, UE can report the above CQI informationaccording to a backward compatible CQI table or a CQI table whichsupports 256 QAM modulation.

The downlink scheduling information receiving unit is configured toreceive downlink scheduling information sent from the base station.

The downlink data receiving and processing unit is configured to,according to MCS information of DCI included in the downlink schedulinginformation, receive and process accordingly downlink data sent from thebase station. Here, UE can process MCS information according to abackward compatible MCS table or a MCS table which supports 256 QAMmodulation.

It can be seen from the above specific implementations of the presentapplication, application of the method and equipment of the presentapplication can generate CQI table and MCS table which support 256 QAMtransmission, and supports selecting utilization of CQI/MCS tables ofthe existing LTE standard or selecting utilization of CQI/MCS tableswhich support 256 QAM transmission according to link status of UE,thereby optimizing performance of downlink transmission.

Various embodiments disclosed herein are provided merely to describetechnical details of the present disclosure and to help in theunderstanding of the present disclosure, and do not limit the scope ofthe present disclosure. Accordingly, the scope of the present disclosureshould be construed as including all modifications or various otherembodiments based on the technical idea of the present disclosure asdefined by the following claims and their equivalents.

What is claimed:
 1. A method for communication by a base station in awireless communication system, comprising: transmitting, to a userequipment (UE), downlink control information (DCI) including informationon a modulation and coding scheme (MCS) for processing downlink datausing an MCS table among a plurality of tables; and transmitting, to theUE, the downlink data, wherein each of the plurality of MCS tablesindicates modulation orders and code rates, wherein the plurality of MCStables comprises a first MCS table which supports 256 quadratureamplitude modulation (QAM) and a second MCS table which does not support256 QAM, and wherein a number of MCS indexes in the first MCS table isequal to a number of MCS indexes in the second MCS table.
 2. The methodof claim 1, wherein MCS items in the first MCS table except at least oneMCS item of 256 QAM are in the second MCS table, and wherein at leastone MCS item, each having a predetermined MCS index, an MCS item of 64QAM with a highest coding rate, and an MCS item having overlappingspectral efficiency with another MCS item in the second MCS table arenot in the first MCS table.
 3. The method of claim 1, wherein if aformat of the DCI is a first DCI format which supports 256 QAMscheduling, the MCS is processed by the UE based on the first MCS table,and wherein if the format of the DCI is a second DCI format which doesnot support 256 QAM scheduling, the MCS is processed by the UE based onthe second MCS table.
 4. The method of claim 1, wherein the informationon the MCS has 5 bits.
 5. A base station comprising: a transceiver; anda controller coupled to the transceiver, wherein the controller isconfigured to: transmit, to a user equipment (UE), downlink controlinformation (DCI) including information on a modulation and codingscheme (MCS) for processing downlink data using an MCS table among aplurality of tables, and transmit, to the UE, downlink data, whereineach of the plurality of MCS tables indicates modulation orders and coderates, wherein the plurality of MCS tables comprises a first MCS tablewhich supports 256 quadrature amplitude modulation (QAM) and a secondMCS table which does not support 256 QAM, and wherein a number of MCSindexes in the first MCS table is equal to a number of MCS indexes inthe second MCS table.
 6. The base station of claim 5, wherein MCS itemsin the first MCS table except at least one MCS item of 256 QAM are inthe second MCS table, and wherein at least one MCS item, each having apredetermined MCS index, an MCS item of 64 QAM with a highest codingrate, and an MCS item having overlapping spectral efficiency withanother MCS item in the second MCS table are not in the first MCS table.7. The base station of claim 5, wherein if a format of the DCI is afirst DCI format which supports 256 QAM scheduling, the MCS is processedby the UE based on the first MCS table, and wherein if the format of theDCI is a second DCI format which does not support 256 QAM scheduling,the MCS is processed by the UE based on the second MCS table.
 8. Thebase station of claim 5, wherein the information on the MCS has 5 bits.